text: At the start of the Renaissance, the nature of alum remained unknown. Around 1530, Swiss physician Paracelsus recognized alum as separate from vitriole (sulfates) and suggested it was a salt of an earth. In 1595, German doctor and chemist Andreas Libavius demonstrated that alum and green and blue vitriole were formed by the same acid but different earths; for the undiscovered earth that formed alum, he proposed the name "alumina". German chemist Georg Ernst Stahl stated that the unknown base of alum was akin to lime or chalk in 1702; this mistaken view was shared by many scientists for half a century. In 1722, German chemist Friedrich Hoffmann suggested that the base of alum was a distinct earth. In 1728, French chemist Étienne Geoffroy Saint-Hilaire claimed alum was formed by an unknown earth and sulfuric acid; he mistakenly believed burning that earth yielded silica. (Geoffroy's mistake was corrected only in 1785 by German chemist and pharmacist Johann Christian Wiegleb. He determined that earth of alum could not be synthesized from silica and alkalis, contrary to contemporary belief.)  French chemist Jean Gello proved the earth in clay and the earth resulting from the reaction of an alkali on alum were identical in 1739. German chemist Johann Heinrich Pott showed the precipitate obtained from pouring an alkali into a solution of alum was different from lime and chalk in 1746.
  German chemist Andreas Sigismund Marggraf synthesized the earth of alum by boiling clay in sulfuric acid and adding potash in 1754. He realized that adding soda, potash, or an alkali to a solution of the new earth in sulfuric acid yielded alum. He described the earth as alkaline, as he had discovered it dissolved in acids when dried. Marggraf also described salts of this earth: chloride, nitrate and acetate. In 1758, French chemist Pierre Macquer wrote that alumina resembled a metallic earth. In 1760, French chemist Théodore Baron d'Hénouville expressed his confidence that alumina was a metallic earth.
  In 1767, Swedish chemist Torbern Bergman synthesized alum by boiling alunite in sulfuric acid and adding potash to the solution. He also synthesized alum as a reaction product between sulfates of potassium and earth of alum, demonstrating that alum was a double salt. Swedish German pharmaceutical chemist Carl Wilhelm Scheele demonstrated that both alum and silica originated from clay and alum did not contain silicon in 1776. Writing in 1782, French chemist Antoine Lavoisier  considered alumina an oxide of a metal with an affinity for oxygen so strong that no known reducing agents could overcome it.
  Swedish chemist Jöns Jacob Berzelius suggested the formula AlO for alumina in 1815. The correct formula, AlO, was established by German chemist Eilhard Mitscherlich in 1821; this helped Berzelius determine the correct atomic weight of the metal, 27.